[IRGen] Fix missing musttail call for dynamic functions.

Author: varungandhi-apple

lib/IRGen/GenDecl.cpp

@@ -2613,7 +2613,12 @@ void IRGenModule::createReplaceableProlog(IRGenFunction &IGF, SILFunction *f) {
       FunctionPointer(silFunctionType, realReplFn, authInfo, signature)
           .getAsFunction(IGF),
       forwardedArgs);
-  Res->setTailCall();
+  if (Res->getCallingConv() == llvm::CallingConv::SwiftTail &&
+      Res->getCaller()->getCallingConv() == llvm::CallingConv::SwiftTail) {
+    Res->setTailCallKind(IGF.IGM.AsyncTailCallKind);
+  } else {
+    Res->setTailCall();
+  }
   if (IGF.CurFn->getReturnType()->isVoidTy())
     IGF.Builder.CreateRetVoid();
   else

test/IRGen/async/run-call-dynamic-void_to_void.swift

@@ -17,6 +17,7 @@ import _Concurrency
 // CHECK-LL: @"$s4main3runyyYFTu" = hidden global %swift.async_func_pointer
 
 // CHECK-LL: define hidden swift{{(tail)?}}cc void @"$s4main3runyyYF"(%swift.context* swiftasync {{%[0-9]+}}) {{#[0-9]*}}
+// CHECK-LL: musttail call swifttailcc void
 dynamic func run() async {
   print("running")
 }